CRABGRASS MARCH 23

Nick Christians
March 24, 2012

I received these pictures from Grad Student Andrew Hoiberg on March 23. They were taken in a very protected area by animal science on ISU campus. I did another check of the areas on campus where I see crabgrass first each year on the morning of March 24 and still see no crabgrass germinating in these areas. I'll keep you posted on other developments.

These are the real thing. It is large hairy crabgrass. Notice the pointed leaf tip and the fine hairs on the leaf margin.

I would like more pictures from around the state as you see crabgrass emerge. I will get them up on the blog. This does appear to be one of the earliest springs in my 33 years here in central Iowa.

KNOTWEED OR CRABGRASS?

Nick Christians

March 23, 2012

The warm weather and the unusually large number of growing degree days (GDD) for late March have led to a lot of concern about early crabgrass germination.

First of all, let me tell you about my experience with this over the past 33 springs in central Iowa. I watch crabgrass germination dates very closely because of my research with preemergence herbicides. I have often been worried about early germination because of warm conditions in March and early April, only to find that cragbrass germinates at about the normal time, around May 1 in the Ames/Des Moines area. This is also true in cooler years when I anticipate late germination may occur later than usual. The germination is still around the normal time.

This year is one of the warmest in my experience and I’ll be watching the situation closely. At the research station we plan to apply applications of Dimension (dithiopyr) and Baracade (prodiamine) separately in test plots on April 1, April 15 and May 1 to determine what kind of crabgrass control we can expect in a warm year like this. I’ll keep you informed of the results as things develop. We will also discuss this work at field day on July 19.

We have had several calls and e-mails in the last few days about emerging crabgrass. I spent March 21 looking for any emerged crabgrass around town and around Veenker golf course. I did not find any. What I am seeing is a common problem at this time of year. Prostrate knotweed (Polygonum aviculare), which is a broadleaf species common in compacted areas around sidewalks and on in the center of sports fields, looks a lot like crabgrass as it emerges. This is one of the earliest germinating weeds in the landscape and is often observed in March and even in late February. While it is a broadleaf, it can look a lot like a grass when it first emerges. It is often mistaken for crabgrass by lawn care customers early in the season. It is a problem for lawn care specialists because the customers will often tell them that they have applied their preemergence herbicide too late. It is not until the leaves begin to mature that it becomes clear that this is a broadleaf and not a grass.

While I found knotweed everywhere I looked on the 21^st, I did not see any crabgrass, even on bare soil on southern exposers where the crabgrass usually emerges first.

I did notice some interesting things about the knotweed. While this species is considered to be an annual in this location, it does appear that some of the runners may not have died during the unusually warm conditions this winter and that leaves were emerging from the runners. That is very unusual. I'm not quit sure of this yet and I will continue to watch this development over the next couple of weeks.

The picture below is of knowtweeed germinating from seed in March.





A close up of the plants shows that it is clearly not crabgrass, but it
does look like crabgrass from a distance.

I also saw quite a bit of annual bluegrass (Poa annua) which usually germinates in fall, but which can germinate in spring. This species can also be mistaken for emerging crabgrass.

The last picture is of an annual broadlef that looks so much like crabgrass that it fooled me when I first saw it. Its texture and color and size exactly matched germinating crabgrass. The main difference is that the leaves are rounded on the end, whereas crabgrass will have more of a pointed leaf tip. I can see how people are easily fooled by these seedlings at this stage, however. I think that these emerging plants are knowtweed, but they are a little different and I'm going to continue to watch them over the next few weeks. If it turns out to be another species, I will let you know in a future blog.

So, what am I recommending as far as the best time to apply preemergence herbicides this spring?

I am currently telling people to go about two weeks earlier than they normally would. If you are used to getting them down by May 1, try to get them down by April 15. The timing will be later in Northern Iowa and earlier in Southern Iowa.

Dithiopyr (Dimension) has some post activity on newly germinated crabgrass and if you have to go later, that may be your best product.

If people call me on May 1 and ask if they should still treat, I'm going to tell them yes. I'm still betting that crabgrass germination will occur close to its normal time.

Poa Annua Seed Head Control at Des Moines Golf & Country Club

This article comes to us from Rick Tegtmeier, CGCS, Des Moines Golf & Country Club.

At DMGCC, we are like many other golf courses in Iowa, we have poa annua and we try to control the ugly seed heads that emerge in the spring. Many different types of growth retardants are used and we are no different. We use a combination of Primo and Proxy to control our seed heads. When we spray it on our fairways we use the following rates of PGR: Primo at 5 oz per acre (.11 oz/1000) and Proxy at 220 oz per acre (5 oz/1000). This is commonly referred to as the 5 and 5 program.

 One thing we all struggle with is to when we start spraying the turf. In the case of poa annua seed heads, control must be done well ahead of the emergence of the seed head from the sheath area of the plant. We have found that using a Growing Degree Calculator has been our best tool to get the timing correct on when we do our first spray. I use a simple Excel spreadsheet to enter my daily temperatures and it automatically figures the cumulative total of Growing Degree Days.

My good friend Steve Cook, CGCS, MG,Director of Agronomy at Oakland Hills Country Club wrote an explanation on Growing Degree Days for his membership and I have included a little bit of that here. One thing to note is to make sure you know what model (base) of GDD calculator you are using. We use the 32 degree base at DMGCC and some people use the 50 degree base. Just make sure your cumulative days match your model!


Here is Steve’s explanation of GDD and how it affects the plant:
The growth rates of many biological organisms are determined by temperature. As temperatures increase, activity increases. One of the ways we measure the biological activity of plants and insects is Growing Degree Days or GDD. Knowing the GDD allows us to monitor a specific number and apply plant protectants (like insecticides) at the appropriate time in an organism’s life cycle to maximize control. It has applications for plants like crabgrass or poa annua as well. What is GDD and how is it calculated? We assume that an organisms growth rate increases as the temperature rises above a predetermined base temperature. Each organism may be given a specific base temperature. Knowing these activity thresholds is important and we monitor them depending on our target pest and optimal treatments.

This year the timing is much earlier than we normally spray. We do 2 sprays in the spring to control those pesky seed heads. There are some studies out there that advise you when to make the second application as well. This too is based on cumulative GDD’s. Until more work is done though, we will continue our program of spraying 21 days after the 1st spray. We typically apply some ferrous sulfate with the 2nd spray to mask some of the PGR effects. If you would like a copy of our Excel Spreadsheet shoot me an email and I would be happy to share it with you.

Rick Tegtmeier, CGCS
Des Moines Golf & Country Club

Time for Primo/Proxy Applications

Forsythia bush in full bloom.  Picture taken March 19, 2012.

The winter season officially ended on Monday. With the mild weather we experienced this offseason, at times it seemed like winter never arrived. Central Iowa saw temperatures climb into the 80’s for five consecutive days last week. According to the National Weather Service, it’s the first time that’s ever happened during the month of March. Four inch soil temperatures are creeping into the low 60’s across most of the state. Forsythia bushes are in full bloom.

So what does this bizarre weather mean to you and your turf? The weather is well ahead of normal and agronomic practices will need to occur sooner than normal as a result. Avoid the temptation to schedule activities solely base on the calendar because this spring has been anything but normal.

Growing degree days (GDD) can help give you an idea of how unusual this spring is shaping up to be. GDD’s are a measure of heat accumulation and are used to predict plant and pest development rates. Daily maximum and minimum temperatures are used along with a base temperature to calculate a GDD value for each day. Below are two maps showing accumulated GDD’s from March 1 through March 20 for 2011 and 2012. As far as GDD’s go, most parts of the state have accumulated 2 to 3 times the number of GDD’s as this same time last year. In fact, it took until April 10 last season to accumulate the number of GDD’s we have experienced so far.

Growing degree day comparison from March 1 to March 20 for 2011 and 2012. 

Michigan State University has conducted research looking at GDD’s for a number of turf applications including Primo/Proxy applications. Their research indicates that the ideal GDD ranges for Primo/Proxy application is 200-500. Our accumulated GDD's indicate that the entire state is within the target range for Primo/Proxy. Now is the time to make your Primo/Proxy application for seedhead suppression of annual bluegrass.

Marcus Jones
Assistant Scientist
Iowa State University

VOLES

Nick Christians

March 15, 2012

Here is a common problem this spring as superintendents remove covers from greens and tees. It is vole damage caused by feeding on bentgrass and other species by these small rodents. It can also take place under snow cover, although we had little of that in the Midwest this winter.

Picture courtesy of Tim Christians at Makray Memorial Golf Club, Barrington, Ill.

Voles are mouse-like rodents with a shorter body, shorter hairy tails, and smaller ears. They are sometimes referred to as field mice in this region. According to Wikipedia, there are approximately 155 species of voles that vary from quite small up to nine inches in length. My guess is that they all like grass. Voles have underground nests and do not hibernate, which means that they have a lot of time in the winter to feed. There are traps, baits and repellents available, but success with these is usually limited.

Fortunately, with a little topdressing and fertilizer, the problem is easily repaired in the spring However, they can certainly be annoying when you first pull the covers off.

Picture courtesy of Tim Christians Makray Memorial Golf Club, Barrington, Ill.